Scala 2.8 HelloWorld程序ClassNotFoundException

Question

我正在尝试运行一个scala程序，

class HelloWorld {
  var myField = 0;

  def getMyField() : Int = {
    return this.myField;
  }

}

即使程序名为HelloWorld.scala我ClassNotFoundException收到ClassNotFoundException

下方完整错误

Exception in thread "main" java.lang.ClassNotFoundException: HelloWorld
    at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Class.java:190)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:122)

好的，查看scala的文档http://www.scala-lang.org/documentation/getting-started.html

我将代码更改为此，

object HelloWorld {
  def main(args: Array[String]) {
    println("Hello, world!")
  }
}

这是现在的错误

Information:24/7/15 10:55 AM - Compilation completed with 1 error and 7 warnings in 2s 32ms
Error:scalac: Error: org.jetbrains.jps.incremental.scala.remote.ServerException
Error compiling sbt component 'compiler-interface-2.8.0.final-51.0'
    at sbt.compiler.AnalyzingCompiler$$anonfun$compileSources$1$$anonfun$apply$2.apply(AnalyzingCompiler.scala:145)
    at sbt.compiler.AnalyzingCompiler$$anonfun$compileSources$1$$anonfun$apply$2.apply(AnalyzingCompiler.scala:142)
    at sbt.IO$.withTemporaryDirectory(IO.scala:285)
    at sbt.compiler.AnalyzingCompiler$$anonfun$compileSources$1.apply(AnalyzingCompiler.scala:142)
    at sbt.compiler.AnalyzingCompiler$$anonfun$compileSources$1.apply(AnalyzingCompiler.scala:139)
    at sbt.IO$.withTemporaryDirectory(IO.scala:285)
    at sbt.compiler.AnalyzingCompiler$.compileSources(AnalyzingCompiler.scala:139)
    at sbt.compiler.IC$.compileInterfaceJar(IncrementalCompiler.scala:33)
    at org.jetbrains.jps.incremental.scala.local.CompilerFactoryImpl$.org$jetbrains$jps$incremental$scala$local$CompilerFactoryImpl$$getOrCompileInterfaceJar(CompilerFactoryImpl.scala:87)
    at org.jetbrains.jps.incremental.scala.local.CompilerFactoryImpl$$anonfun$getScalac$1.apply(CompilerFactoryImpl.scala:44)
    at org.jetbrains.jps.incremental.scala.local.CompilerFactoryImpl$$anonfun$getScalac$1.apply(CompilerFactoryImpl.scala:43)
    at scala.Option.map(Option.scala:145)
    at org.jetbrains.jps.incremental.scala.local.CompilerFactoryImpl.getScalac(CompilerFactoryImpl.scala:43)
    at org.jetbrains.jps.incremental.scala.local.CompilerFactoryImpl.createCompiler(CompilerFactoryImpl.scala:22)
    at org.jetbrains.jps.incremental.scala.local.CachingFactory$$anonfun$createCompiler$1.apply(CachingFactory.scala:24)
    at org.jetbrains.jps.incremental.scala.local.CachingFactory$$anonfun$createCompiler$1.apply(CachingFactory.scala:24)
    at org.jetbrains.jps.incremental.scala.local.Cache$$anonfun$getOrUpdate$2.apply(Cache.scala:20)
    at scala.Option.getOrElse(Option.scala:120)
    at org.jetbrains.jps.incremental.scala.local.Cache.getOrUpdate(Cache.scala:19)
    at org.jetbrains.jps.incremental.scala.local.CachingFactory.createCompiler(CachingFactory.scala:23)
    at org.jetbrains.jps.incremental.scala.local.LocalServer.compile(LocalServer.scala:22)
    at org.jetbrains.jps.incremental.scala.remote.Main$.make(Main.scala:62)
    at org.jetbrains.jps.incremental.scala.remote.Main$.nailMain(Main.scala:20)
    at org.jetbrains.jps.incremental.scala.remote.Main.nailMain(Main.scala)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at com.martiansoftware.nailgun.NGSession.run(NGSession.java:319)
Warning:scalac: /tmp/sbt_20e2573f/compiler-interface-sources/CompilerInterface.scala:161: error: object creation impossible, since method registerTopLevelSym in trait GlobalCompat of type (sym: this.Symbol)Unit is not defined
Warning:scalac:             new Compiler() with RangePositions // unnecessary in 2.11
Warning:scalac:                             ^
Warning:scalac: /tmp/sbt_20e2573f/compiler-interface-sources/CompilerInterface.scala:165: error: class Compiler needs to be abstract, since method registerTopLevelSym in trait GlobalCompat of type (sym: Compiler.this.Symbol)Unit is not defined
Warning:scalac:     class Compiler extends CallbackGlobal(command.settings, dreporter, output)
Warning:scalac:               ^
Warning:scalac: two errors found

Answer 1

您的错误不在代码中，而是在您尝试运行代码的方式中。

我将代码加载到REPL中，没有错误。 我将代码加载到IntelliJ中，并收到很多样式警告，但没有错误。 我编译了代码并从命令行运行它：

%> java HelloWorld
Error: Main method not found in class HelloWorld, please define the
main method as:
   public static void main(String[] args)

这是应该期待的。

Answer 2

我不了解您如何尝试运行程序。 由于我没有任何错误。 让我与您分享一种运行代码段的简单方法。

    class HelloWorld{
       var myField = 0;
       def getMyField() : Int = {
        return this.myField;
      }    
    }

    object Test extends App{
      println(new HelloWorld().getMyField())
    }

尝试通过右键单击Test来运行Test对象。 希望我会有所帮助。

Answer 3

假设您正在运行IntelliJ，请尝试构建项目（CTRL + F9），然后运行它。 我有同样的问题，它对我有用。